Train dispatching system



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l E. J. BLAKE ET AL TRAIN DISPATCHING SYSTEM Filed Aug 27, 1931 TETE;

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6 Sheets-Sheet 2 ATTORNEY Much 159 3.933- E. J. BLAKE Erm. '2,111,352

TRAIN DISPTCHING SYSTEM Filed Aug. 27, 1931 6 Sheets-Sheet 5 ch 15 1938.E. J. BLAKE Er AL,

TRAIN DISPATCHING SYSTEM Filed Aug. l27, 1931 6 Sheets-Sheet 4 I l I lMarch 15, 1938, EI J, BLAKE ET AL '2,111,352

TRAIN DI SPATCH ING SYSTEM Filed Aug. 27, 1931 6 Sheets-Sheet 5 Ira-:zr13.

INVEN OR my @jah BY a MF- Marc-vg ATTORNEY Malh 15, 1938. E, 1 BLAKE E1-AL Y 2,111,352

TRAIN DISPATCHINQ SYSTEM Filed Aug. 27, 1931 6 Sheets-Sheet 6 PatentedMar. 15, 1938 UNITED STATES 2,111,352 TRAIN DISPATCHING SYSTEM'.

Eli J. Blake, Haddonfield, N. J., and Arthur H.

Adams, Yonkers, N. Y.; Elsie A. Blake executrix of said Eli J. Blake,deceased; said Adams assigner to Elsie A. Blake, East r- 'ange, N. J.

Application August 27, 1931, Serial No. 559,671

11 Claims.

This invention relates to improvements in train dispatching systems, andmore particularly to an improved communication arrangement between thecontrol station and the substations connected therewith.

In the train dispatching system to which the present invention isapplied, a control station is connected through a single circuit with aplurality of substations in such a manner that by means of suitableunits, train signaling, track switching, and other traiiic regulatingoperations and the like, may be performed at any one of the substationsin accordance with instructions transmitted from the control station.The control station is also apprised of the track and roadside signalconditions by means of so-called OS indications, i. e., by means ofimpulses 'generated at the control station and affecting indicatorsthereat but modied by the condition of the traffic regulating devices atthe substations. The communication is by coded impulses directing asubstation to perform certain operations or, at the will of the controlstation operator, informing the latter whether instructions have beencarried out at a particular substation. Thus, the control stationautomatically and periodically tests traino regulating conditions at allthe substations, i. e., obtains information on the positions of trackswitches, semaphores, track relays, etc.

If it is desired to effect changes at a substation, the operator at thecontrol station adjusts an impulse transmitter to send code symbolstypical for the desired substation and the operations to be performedthereat. A receiver is provided at each substation but only the receiverof the desired substation shall respond and .actuate the associatedcontrol units in accordance with the code symbols. For the sake ofeconomy and rapidity of communication, the stations are interconnectedby a single circuit over which time channels are established throughwhich various stages of the communicating are performed. A definition ofthis term is given at the end of this specication. In accordance withone embodiment of the invention, the time channels are used inoverlapping groups, i. e., the same time channel may serve in twodifferent codes directed to two different results.

The time channels are used also for the purpose of conveying reportsignals to the control station. The traflic governing devices at thesubstations are associated with the control circuit over certainchannels to actuate receivers at the control station in accordance withcode impulses that have originated at the control station. During thesame channel both control and report symbols may be sent. The faithfulcooperation of the control station and substation equipments is insuredby synchronously establishing the channels through which thecommunication takes pace and making eiiective only those substationchannels through which communication should take place.

It will be obvious to those skilled in the art that the presentinvention may be modified in many respects without exceeding the scopeof the appended claims. The dial and distributing switches may beprovided with contacts that coopcrate with each other in response toother than rotary motions. In fact, any electromechanical circuitswitching arrangement may answer the purpose. The expressions dialswitches,v distributor switches, and the like, were arbitrarily chosenand are intended to apply to any circuit switching device suitable forthe purpose. larly, the connections to the brushes and stationarycontacts of the switches and distributors may be reversed, the lamps,polarized relays and the like replaced by other suitable devices, etc.In the systems herein described, direct current is used for certain, andalternating current for other, phases of the communicating and controloperations. This alsc may be modified and varied to suit particularoperating requirements. The synchronizing arrangements may be replacedby other arrangements which will insure the timely cooperation betweenthe control station and the substations. The rail switches, track relaysand semaphores, which are dened as trai-hc governing devices, may bealtered or supplemented by other traffic governing or testing devices,etc.

These and other departures from the speciiic exempliicaticn of theinvention will be apparent to those who may wish to employ thecharacteristic features of the invention. Most of these features areapplicable to train dispatching systems of widely varying character andneed not be employed in totality.

These and other features are diagrammatically illustrated in theaccompanying drawings, only those parts of a train dispatching systembeing shown which are necessary for explaining to one skilled in the artone manner in which the invention may be practiced.

Fig. 1 shows the relation of the central control station, the line, thesubstations, and the operating units controlled thereby;

Fig. 2 shows in an elementary form means by which communicating timechannels may be established between the central station and eachoperating unit in turn;

Fig. 3 and Fig. 4:, respectively, show arrangements for utilizing thesechannels to control track switch and to control a group of roadsidesignals;

Fig. 5 shows an arrangement for transmitting over one channel a reportindicating the position of an operated unit;

Fig. 6 shows sending and receiving devices at the central stationinvolving further refinements,

Simit whereby a greater number of control or report symbols may betransmitted in a given time;

Fig. 7 shows a detail modification of Fig. 6;

Fig. 8 shows means for maintaining synchronism of the substationapparatus with the central station;

Figs. 9 and 10 show arrangements provided at a substation for receivingcontrol symbols and for characteristically affecting report symbols sentfrom the central station.

Fig. 11 shows a modified system in which direct current impulses aresent for control, and alternating current impulses for report symbols;

Fig. 11a is a detail of Fig. 11;

Fig. 12 is a modification of Fig. 11;

Figs. 13 and i4 illustrate the system in which the time channels arearranged in overlapping groups, and

Fig. 15 is a combination of Figs. 11 and 12.

The same reference numerals occurring in various gures designateidentical or similarly functioning apparatus.

Referring to the drawings, Fig. l is a single line diagram indicatingthe major units involved in the system. I is a central control stationfrom which all other units are controlled and to which their positionsare automatically reported. 2, 3, and 4 are substations scattered alongthe railway route to interpret symbols transmitted from the centralstation and control adjoining groups of controlled or operating units,and to transmit to the control station reports indicating the actualpositions of controlled units. 9 is a control channel which, in thepresent example, is constituted by a line circuit connecting the centralstation to all substations. It is grounded at its far end. I0 is agrounded battery at the central station which originates the energy forcontrol and report symbols.

The central station comprises three sections or substation controlpanels, I2, I3, and I4, on which are localized the control andindicating units for substations 2, 3, and 4, respectively.

At each substation there is a track relay I6, to indicate whether anadjoining track section is clear or occupied. At the top of each centralstation section there is an indicating lampy 49 to indicate the positionof the corresponding track relay. The indicating lamps are located insections of a track diagram to show visually the relation of the sectionindicated to the actual tracks.

At substations 3 and 4 are shown semaphores I'I, adapted to operate inthree positions, viz: vertical, as at substation 3; inclined, as atsubstation 4; or horizontal. In the corresponding sections of thecentral station are control handles 53 having three operating positionscorresponding to the three positions of the semaphores or roadsidesignals; and immediately above are three indicating lamps, one of whichis lit to indicate the position actually occupied by the semaphore.Instead of a single semaphore as drawn at each substation, there may bea group of such adapted to be set up in three combined positions Such as"clear for eastbound movement, clear for westbound movement, and stop.

At substations 3 and 4 there are also power operating machines I 8-I8for operating track switches, and at the central station arecorresponding operating handles 55, 55, each operable to two positionsnormal and reversed; but associated with each operating handle are threeindicating lamps, as in the case oi signal control handles. The leftandright-hand lamps, respectively, indicate that the track switch is closedand locked in its normal or reversed position. The middle lamp indicatesthat the track switch is open or unlocked, which may mean that it is inthe process of throwing over or that it has failed to complete itsstroke and lock up ready for the passage of a train.

Each operated or reported unit I6, I1, or I8 is shown connected to itssubstation by a single wire; but it is understood that any number oiwires necessary for the desired control and reports may be employed.These connections are local and short. In addition to the units I6, I7,and I8, there may be also other traic regulating or indicating devicesassociated with the substations. The single control wire 9 with groundreturn as shown (or with metallic return), is suflicient fortransmitting all necessary control and report symbols between thecentral station and the substations.

At each substation is shown a local battery I9 to furnish power foroperating the track switches, railway signals and reporting mechanisms,subject to control symbols transmitted over the line circuit 9.

One section of the central station is thus actively adapted to control atypical group of railway traffic regulating or indicating unitscomprising one track switch (or group of switches workingsimultaneously), and one roadside signal or group of signals, and alsoadapted for receiving reports which indicate one of three conditions foreach. In addition, it is adapted to receive reports indicating theposition of one track relay. Part of these units may be omitted, as insection I2, or

other units up to the equivalent of the units associated with thetypical section may be included.

Fig. 2 shows an elementary form of means by which a number ofcommunication channels may be established successively between thecentral station and substations. 6 is a motor at the central stationreceiving power from battery I and driving a shaft 20 continuously. 8designates a governor mounted on the shaft comprising centrifugal brakeshoes 5 revolving within a stationary ring I I. At a predetermined speedthe brake shoes are thrown into frictional engagement with the ring IIby centrifugal force and further increase of speed is thereby precluded.

Mounted upon the shaft 20 and insulated therefrom are six movablecontacts or brush arms 2 2 constituting, with the associated groups ofstationary contacts, six dial switches 2l, 22, 23, 24, 25, and 26. A cam2T also mounted upon the shaft 20 controls a follower 28 spring-biasedto- Ward the cam. The follower controls a pawl 29 r which actuates asix-tooth ratchet 37 in such a manner that the latter advances one stepat the end of each revolution of the shaft 20, and completes onerevolution or cycle in six steps. The dial switches 2I-26 perform onecomplete revolution upon each revolution of shaft 20, er six revolutionsper cycle of ratchet 31.

30 -designates a shaft driven by the ratchet 31, and 3l designates asix-point distributor dial switch having its movable contact or brusharm mounted upon the shaft 30 and insulated therefrom. The lastmentioned brush arm is connected to a conductor 9, which is the controlline 9 of Fig. 1. The stationary contacts or segments I, II, III, etc.,of distributor 3I, as the brush arm revolves, connect the line 9successively to the brush arms of dial switches 2|, 22, 23, 24, 25, and26, each of which in turn, during the time it is connected to the line,connects successively with its own group of segments a, b, c,

til

etc. The brush arms of switches 2l, 22, 23, 24, 25, and 26 are alignedto contact simultaneously with their corresponding group of segments.Thus, at the instant illustrated, each brush arm contacts with itssegment a. During six revolutions of the shaft 20 the control line 9will be connected successively to each segment of switch 2l, then toeach segment of switches 22, 23, 2li, 25, and 26 in turn.

66, 6l, 6l), and 68, respectively, are a motor, a battery, a shaft, anda governor, similar to the parts 6, l, 20, and 8 already described, butlocated at a substation along the railway. 63 designates a sleevemounted upon the shaft iiil and driven thereby through friction. Uponthis sleeve are mounted the insulated movable contact or brush larm of adistributor switch 6i and a single tooth ratchet 62. The latter may beengaged by a detent (i5, biased toward the ratchet by a compressionspring 85, or the detent may be disengaged by the energizing of a magnetwinding E9. A second sleeve 8| friction driven from the shaft 60,carries a single tooth ratchet 82 and a cam 64. The latter actuates afollower l2, a pawl 13,

. and the pawl in turn a ratchet i4, similar to the parts 28, 29, and 3lalready described. The ratchet 'i4 drives a shaft 8@ and, by theintervention of friction, a sleeve il) mounted thereon. Upon the latterare mounted the insulated movable contact or brush arm of a six-pointdistributor switch 1l, and a single tooth ratchet i5. After making onerevolution the ratchet (with the sleeve l and the brush arm of 1l isstopped by a spring-biased detent 'i6 until released by current in themagnet coil 11. A second detent S3 is coupled to detent i6 by a link 84and can engage the ratchet 82 only when detent 'i5 drops into notch ofl5, i. e., after six revolutions of ratchet 82 and one ci ratchet l5.When engaged, detent 83 restrains the cam 64 against further movementuntil released by the coil Tl. Current for the coil 'Il is supplied by abattery li and controlled by a polar relay 'i9 in series with the line9, so arranged as to close its contact only when current flows throughthe line from the negative pole of a battery.

Each of the switches 2| to 25 is shown for illustration with ve equallyspaced stationary contact segments and one large space from the fthsegment to the rst. The distributor switch 6l is shown with 'vestationary contact segments all symmetrically spaced in a group. Inpractice, all of these dial switches may have a larger number ofstationary contact groups such as eleven. The governors 8 and 6% are soadjusted that the brush arms they control will advance from the rstsegment a to the fifth segment in approximately equal time, but owing tothe increased space from the fifth segment to the starting point onswitches 2i to 26, they willV be somewhat later in returning to thestarting point than distributor 6I or at least in no case, even with themaximum deviations from normal speed, will the latter arrive at thestarting point later than the f former.

All parts are shown at an instant when the dial switches 2l to 2d havejust reached their starting point on segment a. The cam 21 actingthrough the follower, pawl, and ratchet 23 and and 3l has just advancedthe distributor 3i to the stationary contact segment I, and the line 9is thereby connected through segment a of distributor 2l to the negativepole of battery 54, which is grounded at its midpoint. Before thisinstant, distributors 6| and H at the substation have advanced tosegments a. and I, respectively, establishing a circuit from groundedbattery 54 at the central station through distributors 2i and 3i, line9, the coil of relay 19, distributors 'll and 6I, and through thewinding of starting magnet 69 and the next section of line 9 to thesucceeding substations, and ultimately to ground at the end of the line,as shown in Fig. l. Since the battery connection, as stated, was at thenegative pole, current through polar relay 'i9 is of negative polarityand the relay Contact is closed, energizing magnet 'il by current frombattery 'i8 to release the detents le and 83 which just previously heldthe distributor ll and the cam Ed at theirstarting positions. Thisoccurs at all substations. At the same time, the line current passingthrough magnet SS has withdrawn the detent 65 which just previously helddistributor 6i. This occurs only at one substation at a time: in theillustration it is about to occur at the one shown. Thus at theillustrated substation and instant two independently releasable elementsare started rotating together and in step with central. These are:first, shaft di with stop ratchet 82 and cam Sii, which always revolvessix times per cycle, giving six steps or one revolution to distributor li; second, distributor 6l, which makes one revolution in one-sixth ofthe cycle and is still during iive-sixtns. Because it is contact I ofdistributor 1I that is connected to distributor 6i in the substationshown, the latter makes its revolution in the rst sixth of the completecycle. At the ve other substations distributors 6l would be connected,respectively, to contacts II, III- VL of their respective distributorsli. Distributors Gi in the six substations thus make single revolu tionseach in a different sixth of the full cycle, and in step with one of thesix revolutions of dials 2i-2i. In this revolution line 9 rst connectssegment a. of ti and a of the corresponding central office dial 2i (asshown), or 22, or etc.; then b and bi, etc. Thus in each cycle fiveinstants of electrical continuity (over line S) exist between ve centraloice and iive substation conductors in a xed onetoone correspondence.This is frequently called dividing line time into channels. Timechannels of this kind may be spoken cf and treated like separate wires,with the one limitation that no two coexist in time. Of each ivechannels one (a) being used for the selhprotective purpose of startingsubstation dials in synchronism (more properly, in phase) with centraloffice dials, there remain four to each substation for use, i. e.,twenty-four pay load channels per cycle. Fig. 2 shows simple novel meansfor creating and protecting a number of individual usable channelsbetween one central and each of several subsidiary stations, but withoutregard to how they may be used.

Summarifzing more concretely, dial switches 22 to 2t in turn will beconnected to the control line f8 during the five revolutions in whichdistributor Si is iocked. During each of these revolutions a differentdistributor at a different substation may be connected to the line andmay function and there being set up with each substation as manycommunication time channels, successively established, with the centralstation over line circuit 9, as there are stationary segments on each ofdial switches 2|, 22 to 26, on each distributor 6|.

It should be observed that the negative pole of battery 54 is connectedto the starting segment a only at distributor 2|, while thecorresponding segments of distributors 22 to 26 are connected to thepositive pole of battery. Since the relay 19 and the correspondingrelays at other substations respond only to negative current, it followsthat all revolution counting distributors 1| will be started in stepsimultaneously only during the first revolution of each cycle. Hence,even if. the entire system be thrown out of step (so long as the motors66 continue to run), all substation distributors will run up to thestarting position and stop at some time during the iirst six revolutionsof the shaft 20. At the beginning of the next succeeding cycle all willstart again in unison.

Fig. 3 shows connections which may be made over two channels to controla track switch in two positions. Current passes from ground, throughcentral battery 54, to one of two points of selector switch 55, atcentral station, thence (at the instant when they are connected to theline), over one of two segments at central switch 2| to the control line9, then by one of two segments in substation distributor 6|, through alocal control circuit, to a relay operating coil 86 or 69, and so toground. As shown, 86 was the coil last energized and its Contact linger88 is closed to the front contact where it is held by current passingfrom ground through substation battery I9, through the front contact ofnger 88 to a holding coil 81, thence through a back contact of nger 92oi relay 89 to the normal operating wire 94 of the track switch machine,and so to ground. It is understood that a relay or other contact at thetrack switch machine must remain continuously closed while the trackswitch is in its normal position to maintain current through the holdingcoil 81.

If the selector switch 55 be now reversed and suflicient time elapse forthe switch 2| and distributor 6| to revolve to the correspondingposition, current will pass through the second local control circuit tothe operating coil 89, closing contact 9| and opening contact 92 whichinterrupts the holding circuit through coil 81 and allows back contactat 88 to close. Thus a holding circuit is established from battery |9through fingers 88 and 9| and the holding coil 90 to the reverseoperating wire 93; and in general, when either operating coil 86 oroperating coil 89 is energized momentarily, it interrupts the holdingcircuit of the other relay and establishes a holding circuit for its ownrelay; so that a momentary impulse through the one coil or the otherserves to establish one or the other of the operating circuits, and thecircuit established is maintained until superseded by energizing theother operating coil.

Obviously, instead of two track switch or roadside signal operations,switch 2| and distributor 6| may jointly control three or moreoperations. Fig. 4, for instance, shows roadside signal operatingcircuits controlled over three channels or control wires of selectors 2|and 6|, in accordance with the position of three-way selector switch 53.The diagram shows connections as they exist at the instant when thecontrol circuit is closed through the upper contact of the selectorswitch and the corresponding segments of switch 2| and distributor 6|,to relay operating coil 95. The back Contact at 91 being open,interrupts the holding circuits for relays 98 and |02, which aretherefore deenergized at the same time, and a holding circuit isestablished through the front contact of 91, coil 96, and back contactsat and |06, to eastbound operating wire |09. Operating wire |09 passesthrough any necessary relays (not shown) for establishing a roadsidesignal set up for eastbound train movements, and finally to ground.

If operating coil 98 is energized, the holding circuits for 95 and |02are interrupted at back contacts of |0| and |00, respectively, and aholding circuit for 98 is established through front contact |00, coil99, and back contacts 91 and |05, to the stop operating wire |08 whichpasses through the necessary relays to ground, setting all roadsidesignals at stop. It is understood that the local roadside signal controlcircuits are arranged in accordance with customary railway signalpractice to indicate stop" automatically by failure of current or by anyunsafe local condition. The energized circuit here described serves onlyfor setting the roadside signals to stop by the initiative of thecentral control operator at a time when local conditions would permitthem to indicate proceed.

If operating coil 02 is energized, it causes the holding circuitsassociated with 95 and 98, respectively, to be interrupted at backcontacts |06 and |05. At the same time, it establishes its own holdingcircuit through front contact |04 and back contacts 91 and |00, throughholding coil |03 and operating wire |01 (which includes the necessaryrelays to establish the roadside signal set up for westbound trainmovements), to ground.

Thus any one of the operating coils 95, 98, or |02, when energizedmomentarily, interrupts the holding circuit which may previously haveexisted for one of the other relays and establishes its own holdingcircuit, which holds its contact closed thereafter until released byenergy in another operating coil.

Fig. 5 shows a distributor channel connected for transmitting one of tworeport symbols from a substation to the central station, by the use ofcentral station energy. |09 is a contact inserted in the control line 9when the latter passes through one segment of the distributor 6|. Forexample, |09 may be a contact of track relay |6 in Fig. 1, whoseposition it is desired to report at the central station. At the sameinstant dial switch 2| at the central station connects the line throughthe coil of polar relay |08 (which is of negligible resistance), to thepositive pole of 25volt battery |01, which is grounded at its negativepole. A branch circuit connects the line through 100G-ohm resistance 2to the positive pole of 50-volt battery 54, the negative pole of whichis grounded.

When the contact |09 is open, as shown, there is a single closed circuitextending from ground through battery 54, resistor 2 and distributor 2|to the coil of relay 08, and thence through battery |01, to ground. Thetwo batteries being opposed in this circuit, the net voltage acting inthe circuit is the difference of their potentials, viz.' 25 volts.Resistance of all parts of the circuit other than resistor ||2 isrelatively negligible. Hence the current flowing is 25+1000=0-025ampere, passing upward through the coil of relay |08. The latter is soconnected that current in this direction will throw its moving contactto the left or open position, and the relay is designed to have asubstantial bias toward either operated position, so that it will remainopen or closed as the case may be, until reversed by opposite currentthrough the operating coil. Hence either position established during onemomentary closure of the circuit at distributor 2| persists untilreversed by opposite current during some subsequent closure of thedistributor contact.

If the contact |09 is closed at the instant when the channel illustratedis established, the voltage of the battery |01, viz: 25 volts, will beapplied to the line at dial switch 2| without appreciable interveningresistance. For illustration, the total line resistance is assumed to be500 ohms. The current through the line will be 25+500=0.05 ampere.V Thebattery |01 is holding the switch 2| at a potential 25 volts above theground, irrespective of current flowing. The battery 54 is maintainingits positive pole 50 volts above the ground, or 25 volts above thedistributor. Hence there will be a current of 25+1000=0-025 ampere owinginto the line through resistor H2. The remainder of the line current,viz: 0.025 ampere, must flow downward from battery |01 through the coilof relay |08. Hence the moving contact of relay |08 will move to itsright-hand or closed position and remain there until reversed bycurrent. A circuit will thus be established through battery andindicating lamp H will burn so long as each succeeding revolution ofdistributor 6| and switch 2| finds the contact |09 closed.

As previously stated, reports and indications are desired for threepositions of each track switch and each group of roadside signals. Inthese cases two channels, two contacts like |09, and two relays like IJBmay be employed, each relay following the position of one contact |09.There are thus four possible combinations of open and closed positionsat the two contacts |09, and consequently four combinations of positionsat the two relays |08. By the use of well-known connections of the relaycontacts three of these four combinations may be used to produce thedesired three indications at the indicating lamps.

Referring now to Fig. 6 which shows typical parts of a central controlstation, including refinements providing for more controlled andreporting units within a given time cycle, 20 is a shaft driven ataccurately constant speed (for example, one revolution per 0.2 second),2|, 22, 23, 24, 25, and 26 are six dial switches mounted on (andinsulated from) the shaft 20, each consisting of a revolving brush arm eand a group of nine contact segments or spaces lettered a to z'. Thebrush arms z are so positioned that all make contact simultaneously withsimilarly lettered segments (or blank spaces) for example, at theinstant illustrated by Fig. 6, each brush arm is in contact with itssegment g. No means for driving the shaft 20 are shown. It may begeared, for example, to a motor provided with a centrifugal brake tolimit it to a definite speed.

30 is a second shaft advancing one step for each revolution of the shaft20, three steps constituting a complete revolution of the shaft 30. Nomeans for driving the shaft 30 are sho-wn, but many well knownmechanisms are available for the purpose, such as a three-tooth ratchet,a pawl and a cam on the shaft 20 adapted to move the pawl at the end oieach revolution of 20, advancing the ratchet by one tooth; or a sourceof continuous torque applied to the shaft 3U, a three-tooth escape wheelon the shaft, and an escapement actuated by the shaft 22 to permit onetooth advance for every revolution of the latter shaft. Mounted on theshaft 30 and insulated therefrom are three brush arms z associated withdistributor dials 3|, 32 and 33.

9 is the control wire extending throughout the controlled territory andgrounded at the far end. A double throw manually operated switch 40connects the line at will to the brush arm of dial 23 (as shown) ordirectly to the segment w, f of the same dial, and thence to the brusharm of dial 33. At the instant illustrated, and the position illustratedfor switch 40, the line is connected through segment g, i of dial 23through neutral relay coil 4| and polar relay coil 42, to the positivepole of battery 44. The battery is also connected through a coil 43opposed to the coil 42, and throughan artificial line or resistor 45 toground. At the instant illustrated (and as described hereafter), theline 9 traverses a loop circuit associated with one controlled un' (at asubstation) this loop having three con itions, each indicating one stateof a controlled unit (e. g., a semaphore) at this substation, viz:closed through low resistance, closed through high resistance, and opencircuit. In the case illustrated, assume the loop circuit connected intoline 2 is in the rst condition; current passing from battery 44 throughrelay coils 42 and 4| to the line is a maximum. The resistor 45 is soadjusted that the magnetizing force exerted by the coil 42 under thiscondition exceeds that exerted by the constant current passing throughcoil 43 to the resistor; and the upper contact of the polar relay isclosed. The upper, or energized, contact of the neutral relay 4| is alsoclosed.

The high resistance in the second condition of the loop circuit is sochosen that it will reduce the magnetizing force, due to line currentthrough the coil 42, to a value less than that in coil 43, with theresult that the lower contact of the polar relay will close, but theneutral relay 4| will still be closed at its upper contact. However, ifthe line circuit is broken at the substation loop, both relays will beclosed at their lower contacts.

The upper points of relays 4| and 42 are connected to the positive poleof battery 52 and the lower points to the negative pole, the midpoint ofthe battery being grounded, so that the moving contacts are positivewhen up, negative when down. At the instant illustrated the movingcontact of the polar relay is connected through brush arm e and segmentg` of dial switch 2|, through coil of polar relay 45 and through segmentI and brush arm .e of distributor dial 3i, to ground. The polar relay 46is designed to have a substantial bias toward its last operatedposition, so that either contact when closed remains closed untilreversed by reversal of current in the operating coil. So long as thecircuit just described is maintained, the relay 46 is closed to itsleft-hand contact when the upper contact of 42 is closed, and totheright-hand contact when the lower contact of 42 is closed. If theoperating circuit through 46 is then interrupted, its contact remainsclosed at the last operated position until the operating circuit isreestablished with the contact of relay 42 in the opposite position.

In like manner, the moving contact of relay 4I is connected through thebrush arm and the segment g of dial switch 22, through the coil of polarrelay 4l and through segment I and brush arm e of distributor 32 toground. At the instant illustrated, when the dials 2| and 22 are closedthrough segments g-g and the distributor dials 3| and 32 are closedthrough segments I, I, the polar relays 46 and 41 thus assume positionswhich repeat the positions (at that instant) of relays 42 and 4|. Whenthe distributor and dial switch arms vhave moved on to other segments,the relays 46 and 41 maintain their operated positions until the nextoccasion when their operating circuits are closed through segments g-gand I-I.

The moving contact of relay 41 is connected to the positive pole ofbattery 48, the negative pole 'being grounded. The right-hand stationaryconn tact is connected through an indicating lamp 49 to ground. Theleft-hand contact is connected to the moving contact of the relay 46 andthence, according to the position of the latter, either through theright-hand contact and indicating lamp to ground, or through theleft-hand contact and indicating lamp 5| to ground. Since the relays 46and 41'repeat the positions of relays 42 and 4|, and since the latterare dependent on the resistance of the loop circuit which is connectedat that instant in the line, the indicating lamps 49, 50, and 5|indicate the connection (or absence of connection) through the loopcircuit at the instant when connections are established as described; ifthe loop circuit is open, neutral relay 4| will be down and indicatinglampi 49 will light; if the loop circuit is closed through highresistance, relay 4| will be up and relay 42 down, under which conditionindicating lamp 50 will light; if the loop circuit is closed through lowresistance, relays 4| and 42 will be up and indicating lamp 5| willlight. Furthermore, after the operating circuit through the coils ofrelays 46 and 41 has been interrupted at the distributor dials 2|, 22,the lighted lamp will continue to burn until the operating circuit isreestablished, at which time the resistance of the substation loopcircuit will again determine which of the three indicating lamps shalllight.

As described, the indicating lamps 49, 50, and 5| are controlled byoperating circuits extending from the segments I--I of distributor dials3| and 32 to segments g-g of dial switches 2|, 22. Similar circuits mayextend from the segments I-I to each of the pairs of segments g--g toz'-z', controlling three groups of lamps successively as the brush armsz-z of dials 2, 22 revolve. At the end of one revolution of the brusharms of dial switches 2| and 22, the brush arms a of distributors 3| and32 will advance to segments II-II. From these segments three other pairsof operating circuits, controlling three other groups of indicatinglamps, may extend to the segments Q--g to ii of distributor dials 2| and22. Three other groups of indicating lamps may be controlled by circuitsterminating on the segments III, III of distributor dials 3| and 32, sothat we may have in all three times three or nine groups of indicatinglamps controlled by the line circuit 9 successively as the distributorbrush arms revolve. If nine substation loop circuits are successivelyconnected in the line, each group of the nine groups of indicating lampswill indicate the condition of the corresponding substation loop circuitwhen last connected, thereby indicating the position of thecorresponding operating unit which controls that loop circuit. In thecase of operating units having only two positions, such as track relays,the high resistance connection at the loop circuit may be omitted,together with relay 46 and indicating lamps 50 and 5|. 'I'he tworequired indications will then be produced by open and closed conditionsof relay 41, resulting in dark and light indications at the lamp 49.

Instead of receiving reports to indicate the position of operating unitsat the substations,

it may be desired to transmit control signals or symbols to change theposition of one or more controllable operating units. The manualswitches 34, 35, 40, and 56 will then be thrown to the right. Switches34 and 35 will open the control circuits for all indicating lamps.Switch will be instrumental in transmitting a symbol to render thedesired substations receptive to control symbols as described hereafter,and switch 4|? will connect the line 9 through segment af of distributordial 23 to the brush arm a of distributor 33. At the instantillustrated, line 9 will be connected through segment of the dial 23 andsegment I of dial 33 to the brush arm of distributor dial 24 and thenceover segment g to the upper blade of three-position control switch 53.When the brush arm of distributor dial 24 advances to segment h, thecircuit will be transferred to the lower blade of control switch 53.Thus in the two successive time channels in which the brush arm of dial24 makes contact at g and h, respectively, the control line is connectedfirst to the upper and then to the lower blade of the manual switch 53.According to the position of the latter, it is connected to the positiveor negative pole of battery 54 or to neither in the following order:

Upper position: Neither-negative; Middle position: Negative-positive;Lower position: Positivepositive As described hereafter, receivingelements at a substation are arranged to respond selectively to thesethree combinations of current during two time channels, establishing adistinctive roadside signal or semaphore indication in response to eachcombination.

. Similarly, segment i of dial 24 may be connected through manual switch55 to the positive or negative pole of battery 54, and transmits apositive or negative current impulse over the control line to select oneof two possible operations of another controlled unit at a substation.Similar branch circuits, including other control switches, may extendfrom segments g, 71 and i of dials 25 and 26. During three successiverevolutions, as the dials 24, 25, and 26 are connected successively tothe line through dial 33, nine control channels will be established. Onetwoposition operating unit, such as a track switch, may be controlledover any one of these channels; any three-position unit, such as a groupof roadside signals, requires to be controlled over two such channels.

All of the connections thus far described have involved only segments g,h, and i of dials 2| to 26. During the passage of the brush arms overthese segments, the line may be connected, according to the position ofmanual switch 40, to the relays 4| and 42 for receiving report symbols,or through dials 24, 25, and 26 to the control (such as 53, 55) switchesfor transmitting control symbols. During the contact periods at segmentsa to f, the line is connected to dial 33 irrespective of the position ofmanual switch 40, vand through one of dials 33 to dial 24, 25, or 26.

The iirst segments a are preferably separated from the last segments z'by an angle slightly greater than that between other segments. Segmentsa. of dials 24, 25, and 26 are permanently connected to positive batteryand serves to start all substation distributor dials simultaneously foreach revolution as described hereafter.

At each of the dials 24 to 26, two of the three segments b, c, and d areconnected to positive or negative battery. The combination of positive,negative and dead segments at each dial is peculiar to that dial onlyand constitutes a calling code for one substation which is arranged torespond only to signals transmittedl by that particular dial. While Ihave shown only three dials, 24, 25, and 26, each arranged to call onesubstation, it vshould be noted that additional dials, withcorresponding segments on the dials 3| to 33, may be provided for anyrequired number of substations. The three segments b, c, and d assignedfor calling codes will suffice for twelve distinct codes, viz: codesinvolving three choices of one dead channel and four combinations ofpolarity on the remaining two segments. To utilize fully these vtwelve.possible codes (since three-contact distributor 33 can divide line timebetween only three code sending dials like 24, 25, 26), a twelve-contactdistributor must replace 33 and nine more dials like 24, 25, 26 must beadded, but each having its b, c, d contacts differently connected.Distributors 3l and 32 also need twelve contacts each, to provide forenough sets of indicating lamps for twelve substations. If the threecalling code segments b, c, d are increased to four, there will be sixchoices of two dead segments, or twenty-four distinct codes in all. Ifthe number of control and report segments on dials 24, 25, etc., beincreased from three (viz: g, h, i) to nine, each calling code mayestablish communication with a group of three substations instead ofone. Thus, by increasing the total segments on each dial 24, 25, etc.,from nine to sixteen, and by adding the necessary dials and terminalequipment at the central station, the system is adapted to controlseventy-two substations instead of three.

If it is desired to transmit one or more control symbols immediately,without awaiting the moment in the automatic cycle when the controlledunit in question would be connected to its manual control switch at thecontrol station, the shaft 3D carrying the distributor dials 3l to 33may be advanced manually to the position corresponding to the unit to becontrolled and held there during one revolution of the shaft 20. Thedial selected by the master dial 33 will transmit the calling code forthe desired substation and establish the necessary local channels forexchanging report or control symbols.

The segments f of dials 24-26 are connected through manual selectorswitch 5S either to the negative pole of the battery 54, as shown, or tothe positive pole. The former connection constitutes a symbol toestablish reporting loop circuits at the substations called, and therebyto control indicating lamps-such as 49, 5t, and 5l at the centralstation. The latter connection, always accompanied by the right-handposition of manual switch lli), (since tu and 56 are rnechanicallyinterlocked) establishes connections at the central station and thecalled substations for transmitting and receiving control symbols tooperate the controlled units. The segments e are permanently connectedto an alternator H3. Their function is to bring all distributors in thesubstations into step with switches 2l to 26 at central, irrespective oftheir previous position,

as described hereafter. They also correct any small variation fromsynchronism which may have occurred since the previous correction bysegment a. This latter function is unnecessary with nine segments perdistributor as drawn for the sake of clearness, but desirable if a largenumber of segments is used.

It will be observed that the resistor 45 connected to the polar relaycoil 43 corresponds in part with the articial line or balancingnetwork'employed in certain duplex telegraph systems, but differs inthat it is not required to balance the line characteristics but merelyto produce an effect less than that of the normal line impedance andgreater than the line impedance when the latter has been increased toseveral times its normal value. For this reason a plain resistance asshown, traversed by a constant current, will ordinarily suffice.However, in cases where exceptional line constants make it desirable,the resistor may be replaced by any well--known type of artificial line,as indicated at it in Fig. '7. The battery current may then be cut offafter each step and reapplied simultaneously during each channel, y, It,z', both to the physical line 9 and the articial line 45, by a dialswitch l5 revolving in step with dials 2l and 22 of Fig. 6. This meansfor simultaneous application of battery to both lines provides for quickbalance (high speed and short channels) even in cases where the lineconstants of inductance and/or capacitance are unusually high.

Fig. 8 shows means provided to insure that a substation distributor t!will get in step with the switches 2i to 24 of Fig. 6, even if thrownout of step. Sil is the shaft which carries a single tooth ratchet b2and the brush arm of distributor 6I. It is driven at approximatelyconstant speed; for example, by a motor and governor similar to 66 and68 in Fig. 2, but through a friction coupling (not shown, but see Fig.2), which permits the shaft t@ to be stopped by the ratchet 62 withoutstoppage of the motor. The speed is so adjusted that the brush armtraverses the segments a to e and f to i, substantially in step withdial 2| vto 24 (Fig. 6). The spaces e to f and i to a are shorter thanthe corresponding spaces on dial switch 24. Thus distributor o! willalways make contact at segments f and u.` somewhat before thecorresponding contacts are closed at switch 24. A spring i;

biased pawl lt is located to stop the ratchet t2 at the instant when.distributor 6l connects the line to segment e. A magnet ll is providedto release the pawl 'i6 and is connected through a condenser lll to thesecondary of transformer 55 l ifi, the circuit being tuned to respondselectively to the frequency of the alternator l i3 (Fig. 6). A momentafter distributor 6l has stopped with its brush arm connecting thecontrol line to segment e, dial switch 2d at the central station willconnect alternator H3 through its segment e to the line. Alternatingcurrent passing over the line and through segment e of distributor 6Iwill traverse the primary winding of transformer H4 and thence flow overthe continuation of control line 9 to the next substation, andultimately to ground at the end of the line. Current thereby induced inthe secondary of transformer I I4 will cause the magnet 'il to releasethe pawl 16, permitting ratchet 62 and distributor 6| i to start in stepwith switches 2| to 26.

Even if distributor 5l is entirely out of step, as for example, when thesystem is first started in operation with the distributors in randompositions, it will revolve to segment e at some time within its rstrevolution. There it will be held by the pawl 16 until it is released bycurrent to which the magnet 11 is responsive. This can occur only whenswitch 26 connects the line over segment e to the alternator |I3, sincecurrent of the required character is supplied at no other segment.Hence, even under the condition assumed, distributor 6| will start itssecond revolution in step with switches 2| to 26.

When the distributor 6I has advanced until its brush arm makes contactat segment a, it will be stopped again by engagement of the ratchet 62with the pawl 65, adapted to be released by current through the magnet69. A moment later dial switch 24 at central will connect the linethrough its segment a to positive battery. Current will then flow overthe control line and through segment a of distributor 6 I, through coilsI I5 and I |6 and magnet 69 to the continuation of control line 9, andso through succeeding substations to ground at the end of the line. Themagnet 69 being thereby energized will release the pawl 65 and permitthe distributor 6I to start again in step with distributors 2| to 26.The coils ||5 and I|6 are for a purpose described hereafter.

The second starting pawl 65 just described serves to correct anyvariation from synchronism which may have occurred during approximatelyone-half revolution, but is not capable of bringing the commutator intostep from a random position as may be done by the pawl 16, for thereason that it is responsive to direct current received through segmenta of distributor 6|, whether the current originated at segment a ofswitch 24 or at any other segment.

As previously described, the segments b, c and d of switches 24-26 (Fig.6), are used to transinit over the line during each revolution adistinctive symbol calling only such substations as are required torespond during that revolution of switches 2| to 26, the symbolconsisting of positive or negative current on two of the three channelsb, c, and d; and the segment f, together with manual switch 56, servesto transmit positive current over the line when control symbols are tobe transmitted from the central station and negative current when reportsymbols are to be transmitted from the substation.

Fig. 9 shows the means provided at the substation for giving effect tothese calling and selecting symbols.

At 6I is shown a portion of the distributor 6| of Fig. 8. At thestarting segment a` positive current supplied by the central stationpasses through the line 9, through coils I I5 and I I 6, andthe startingcoil 69 (see Fig. 8 also) through the outgoing portion of line 9 tosubstations beyond and ultimately to ground at the end of the line. Thecoils I5 and I I6 are operating coils of two polar relays biased tomaintain their last operated position and are connected in each case tomove the contact to its open position so that the relays are opened atthe start of each revolution of the distributor. I8 and ||9 areadditional operating coils on the same relays, connected, respectively,(in the case shown) to segments b and c of the distributor and tothe-outgoing section of control line 9. It will be recalled thatchannels b, c, and d are reserved for the (twelve possible) callingcodes of the system shown. Incidentally, the code or symbol necessary tocall the one substation shown in Fig. 9 is not one of thosesent by dials24, 25, 26, as shown in Fig. 6. Since the relays are opened at thestartof` each revolution, i. e., during channel a, they can both be closedonly when the channels b and c have been energized during a givenrevolution by current of the particular polarities required to close thecontacts |20 and I2I; in other words, both contacts will be closed onlyduring that particular revolution when the calling symbol which includesthese two channels and this polarity combination is transmitted from thecentral station.

When closed, during one particular revolution, as described, thecontacts I 20 and |2| establish and maintain during that revolution onlya local circuit from grounded battery I9, to a polar relay contact |23controlled by a coil 22 which is connected in series with the controlline 9 during the channel established by the segments f of dial switches24 and 6|. If positive current is received during this channel, contactfinger |23 will swing to the left as shown, completing the local circuitthrough neutral relay |24 to ground, to set up circuits for receivingcontrol symbols during the remainder of the revolution. If negativecurrent is received, finger |23 will swing to the right and complete thelocal circuit through neutral relay coil |25, which sets up loopcircuits for characteristically affecting report symbols during the nextfew channels.

Fig. 10 shows segments g to i of distributor 6| and loop circuits placedin series with the control line 9 through these segments duringsuccessive operating stages of the distributor, either to receivecontrol symbols or characteristically to affeet report symbols, viz:from segment i through polar relay coil |26 or through report switch |32to the outgoing portion of control line 9; from segment h through polarrelay coil |28 or report switch |33 to the same point; and from segmenty through polar relay coil or report switch |35 to the same point. Therelay coils |26, |28, and |30 are bridged by back contacts of relay |24,which is shown energized in Fig. 9. The back contacts are therefore openand current through the loop circuits must traverse the coils. Reportswitches |32, |33, and |35 are bridged by back contacts of relay |25which is shown deenergized in Fig. 9. The report switches are thereforeshown short-circuited and ineffective.

Line current through the channels g, h, and i respectively, traversesthe relay coils |30, |28, and |26 and determines the positions whichtheir respective contact fingers I3I, |29, and |21 will assume, andwhich (by virtue of inherent bias toward their operated positions) theywill maintain until reversed by opposite current in their operatingcoils. Thus the position of the contact lingers |3I, |29, and |21 isdetermined by the polarity of line current through the correspondingchannels g, h, i in that revolution of dial 6I after relay |24 has beenenergized as described by the calling symbol for this substation. Thecoils |26, |28, and |30 are connected to close their respective contactfingers downward when the current through them is positive, upward whennegative. As shown, the finger |21 has last been actuated by positivecurrent and is down, connecting the local battery I9 to the reverseoperating circuit |38 for the track switch. Had negative current beenreceived in channel i, finger |21 would have been up energizing thenormal track switch operating circuit |31.

Operating coil |28, as shown, has last received negative current overthe lower blade of control switch 53 (Fig. 6) and channel h, and itscontact nger |29 is therefore up, energizing local control wire I 39toset up roadside signals for east- Civ bound traic. This occursirrespective of the position of iinger iti; but when finger |29 isclosed downward by positive current in its operating coil, it interruptsthe circuit to the eastbound wire and connects the battery i9 to contactiinger E35. The up or down position of the latter, according as positiveor negative current owed through coil im during channel g determineswhether battery will now gc on local wire lil that sets the roadsidesignals for westbound trafiic, or on local wire Mil that sets them toStopn Response to control symbols over channels g, h, and i, as justdescribed, was dependent upon the previous receipt of positive currentthrough manual switch G (Fig. 6) and channel f, causing contact finger|23 (Fig. 9) to close at the left and energize relay EM. When the manualswitch 5t is closed to the left, as shown in Fig. 6, negative currentwill flow in channel f, and contact finger |23 will close at the rightand energize relay |125. The relay coils |26, E28, and i3d will then beshort-circuited by contacts of the deenergized relay |26! and thereforerendered ineffective; but the contacts of relay l25 will be open and theimpulses sent during channels g, h and i, respectively, wili becharacteristically affecte-d by the positions of report switches |32,E33, and |35. Report switch |32 may be, for example, a contact of atrack relay used to indicate whether a track circuit is clear oroccupied. When open, as shown, it will cause an indicating lamp such as4S) in Fig. 6 (but controlled over channel i) to light. When closed, itwill cause the lamp to be extinguished.

Report switch i3d may be actuated by the mechanism of a track switchoperating machine, and when closed through the line resistance only, asshown, it may indicate that the track switch is closed and locked in itsreverse position. An indicating lamp similar to 5i (Fig. 6) will then becaused to light. When closed through high resistance G3i-i it mayindicate that the track switch is unlocked. An indicating lamp similarto 50 will light. When open it may indicate that the track switch isclosed and locked in its normal position and may cause the indicatinglamp corresponding to d@ to light.

In like manner the report switch |35 may be actuated by a roadsidesignal mechanism, or equivalent circuits may be closed through relaysassociated with the roadside signals, and the three resulting conditionsin the loop circuit, viz: open, closed through high resistance, andclosed through normal line resistance may control the set of indicatinglamps associated with channel g at the central station. The threeindicating lamps associated with channel g and report switch |35 mayindicate, respectively, that the signals are set up for eastboundtraiiic, set up ior westbound traffic and set at stop.

In resum, i. e., of the Figs. 6 to l0 disclosure, using dial switches ofonly nine positions, as shown in. Figs. 6 to l0, there could be handledtwelve substations (three shown), central being able at each to controlone track switch (or group of such) to two positions and one roadsidesignal (or group of such) to three positions; central also receivingcontinuously from each in succession (except when sending controlsymbols or codes), automatic reports about one track switch. (or group)having three connections, about one y roadside signal (or group) havingthree conditions, and about one track relay having two conditions.

Nine time channels to each substation, set up by the synchronousoperation at central and at substations of nine-position revolving dialswitches, are shown utilized as follows:

Positive on channel a starts off all substation dials in step withcentral. (Fig. 8, magnet E9 and detent 65). substation dials gainslightly on central, so will be already stopped, and will start eachcycle exactly with central. This impulse on a also restores to normal oropen contact condition (wiping out the influence of past codes), the twocode receiving polar relays at all substations, (|29 and |2|, Fig. 9).It is by the twelve possible combinations of polarities in each of thesetwo relays with their connections to the three time channels b, c, d,that each substation is differentiated from the others and is adapted toanswer just one of the twelve symbols or codes.

Positive and/or negative impulses on channels o, c, d, constitute thesubstation selecting symbols or codes. Each one of these (twelvepossible) is determined by the positive or negative battery connectionson two out of the a., b, c, segments of dials 24, 25, etc.

Alternating current on channel e puts all substations in synchronismwith central, even if badly displaced. f-

Positive or negative goes out on channel f, according to the right orleft position of manual switch 56', and this choice determines whetherthe impulses to be sent on channels g, h, z', shall cause movement ofroadside signals, track switches, or the like, or shall light indicatinglamps at central to report conditions of the track switch, track relay,semaphore or the like.

Channels g, h, when manual switch 56 is in the right-hand or controlposition, carry the codes that actually determine motion of roadsidesignals at the selected substation. As illustrated, only three codes aresent on g, h, (eight are possible, using either of two polarities oneither or both of two channels). More are not needed to control roadsidesignal conditions and would complicate substation receivingarrangements.

Channel i, with manual switch 55 in righthand control position, carriesa two-unit code (positive or negative) to set the track switch to normalor reverse.

Channels g, h, i, when manual switch 5S is in left-hand or reportposition, carry no codes but are used as mere individual channels forconnecting a battery at central to individual substation loops, eachassociated with a track switch, a roadside signal, or a track relay,during which connections these three loop impedances are compared,individually, to an artiiicial line at central and their conditionsindividually recorded at central on lamps.

Fig. 11 shows a modied system in which positive and negative directcurrent impulses during three time channels transmit the necessarysymbols to control the operating units at one substation, and in whichalternating currents superposed on the direct current during the sametime channels transmit the necessary report symbols to indicate at thecentral station the existing positions of the operating units. As inFigs. 6 to 10, the central station automatically transmits a program ofseveral cycles, each of which includes a, calling signal for one or moresubstations, followed by the necessary channels for control and reportsymbols at the called substations; and provision is made for manuallyadvancing the program to any particular cycle if immediate communicationwith the corresponding substations is desired. The calling code in eachcycle consists in current flow during three among seven channelsassigned for this purpose; and completion of the appropriate callingcode automatically starts the receiver at the called substations in stepwith the central station transmitter,

In some applications of this invention, the control line will extend formany miles and have a resistance of a thousand ohms or more. Certainmagnet windings at all substations are required to functionsimultaneously. If all of these windings were connected to the line inmultiple, the required resistance of each winding for ecient operationwould be much higher than is readily attainable. Therefore, allsubstation windings are shown connected serially in the line, underwhich condition the most eicient resistance values are easilyattainable. On the other hand, contact devices are required in certainsubstation circuits Which function one at a time to transmit reportsymbols. I'hese circuits are shown as branches from the line to groundin order to keep the line clear of the large number of contacts inseries which it would otherwise include.

We have chosen to illustrate a substation receiver and transmitter whichis coupled to the line only by the branch circuits for report symbolsalready mentioned and by two magnets which serve to translate lineimpulses into mechanical movements. All necessary functions ofinterpretation and selection are accomplished mechanically by thesemovements. However, it will be readily understood that the samefunctions could be accomplished by a dial switch and a group of relayssimilar to those shown in Figs. 8 to 10.

2|, 22, and 23 in Fig. 1l are three dial switches at the centralstation, driven at uniform speed by a common shaft 20. 3| is athree-point dial switch arranged to connect the brush arms of dials 2|22 and 23 successively to the control line 9. It is advanced one stepautomatically at the end of each revolution of dials 2| to 23 by cam 21,follower 28 and pawl 29 acting on ratchet wheel 31, as shown in Fig.11a; but a slip coupling F in its driving connection permits of manualsetting by knob K to connect either dial to the line when desired. Eachof the dials 2| to 23 has eighteen segments lettered from a to T. Thesegments shown as White circles are always energized with eitherpositive or negative potential, whereas the black circles representsegments which .are always dead. On each dial, nine segments a, to i,transmit a calling signal for the substations associated with that dial.Segments a and i are dead on all dials, and serve to mark the start andnish of the calling signal. Of the seven intervening segments, adistinctive combination of three segments is connected to positivebattery and constitutes the selective calling symbol for the associatedsubstations. 'I'hree dials are shown, distinguished by three callcombinations, viz: bod, bcc, and bcf; but thirty-five combinations ofthree segments among seven are available, so that the seven callingsegments will sufiice for any number of dials up to thirty-five.

Each of the segments :i to r is energized through a transmitting andreceiving channel as described hereafter, but the connections areindicated only for segment r of dial 2|.

As the brush arms of dials 2| to 23 connect control line 9 to each livesegment in turn, direct current ows from battery 54 over the controlline to condenser |51 at the first substation. Since it is blocked bythe condenser it takes a shunt path around it through the coils of polarmagnet |63 and neutral magnet 69. In the same manner it traverses themagnet coils of each substation in turn and finally goes to groundthrough a network |58|59 at the end of the line and returns through theearth and through alternators |42 and |43 to the center of battery 54.During certain time channels polar magnet |63 selects local operatingcircuits in response to control symbols received over the line. Neutralmagnet 69 and associated parts respond selectively to calling codestransmitted during channels a to z' by the central station dialswitches, and start sending and receiving elements for report andcontrol signals only during those cycles which include the distinctivecalling code for this substation. Magnet 69 releases with a slight timelag sufficient to bridge the interval between two successive livechannels, even when they are of opposite polarity, but must releasepositively when current is interrupted for the duration of one timechannel. If necessary mechanical and electromagnetic inertia do notproduce the required time lag, the electromagnetic inertia may beincreased by well-known means such as a short-circuited path surroundinga por tion of the pole face.

|56 is a shaft driven by local energy at slightly more than tworevolutions per revolution of central station dials 2| to 23, and hencecompleting one revolution in slightly less than nine time channels. |60,I6 and |62 are a group of Wheels rigidly coupled one to another andfrictionally coupled to shaft |56, upon which they are mounted. |64,|65, |66, and |61 are four pawls attached to a common rock shaft |68 andjointly actuated by neutral magnet 69. When the latter is energized,pawl |64 engages the single tooth of wheel |60; when it is deenergized,pawl |65 engages the three intermittently spaced teeth of wheel |6|.During nine successive channels y' to r in each cycle transmitted fromthe central station, magnet 69 will be energized. Irrespective of itsprevious position, wheel |60 will be stopped by its pawl at some timeduring this period, and will be released at the first dead channel, a.Thereafter its progress will depend upon wheel |6I. If live channelsoccur coincidently with the points of engagement for the three teeth ofthis wheel, the three wheels |60, |6|, and |62 will advance withoutinterruption until Stopped again by pawl |64 at live channel 9'. Forteeth as drawn, this condition will obtain during the cycle transmittedby dial 2 in which b, c, and d are live channels. In this case theprojection on wheel 62 will lift follower |69 during channel i andthereby release pawl |10 to which it is coupled by rock shaft |1|. Ifany other calling code than bcd is received, wheel |6| will be delayedat one or more of its three teeth, and cam wheel |62 will release pawl|10 during one of the live channels y' to 1".

|1| is a sleeve mounted upon shaft |56 and frictionally driven thereby.Upon it are rigidly mounted three toothed wheels |12, |13 and |14, abrush arm of dial switch 6|, and a cam |15. Wheels |12 and |13,respectively, are engaged by pawls |66 and |61, actuated by magnet 69.Wheel |14 is engaged by pawl |10. After any group of nine live channels7 to 1' these wheels will occupy the position shown with wheels |12 and|111 engaged by their respective pawls, and can be released only whenboth pawls are released simultaneously. Pawl |66 is released only duringdead channels, and pawl |1|l .at a time dependent upon the progress ofwheels |66, |6|, and |62. As already stated, this time is time channelz' during cycles in which the distinctive calling code for thissubstation is received, and one of the live channels y' to r during allother cycles. In the former case, pawls |66 and |10 will be releasedsimultaneously and sleeve |1| will be allowed to start. In the lattercase, the sleeve will remain locked by pawl |66 at the time it isreleased by pawl |18. In other words, the sleeve will start if thedistinctive call for this station has been received, and not otherwise.At other suhstations having other tooth arrangements on the wheel |6|,sleeve |1| will start responsively to other calling codes.

As in the cycle transmitted by dial 2|, the dead channel may be precededby other dead channels. In this case pawl |66 will have been previouslyreleased when pawl |16 is released by the appropriate calling code. Thestarting time for sleeve lli will depend solely upon wheel |62, andultimately upon the speed of shaft |56, after the release of wheel |60eight time channels earlier. In order to correct the slight gain ofshaft |56 during this time with respect to the time channels of lineimpulses, pawl |61 is arranged to engage wheel |13 and stop it at aposition corresponding to time channel y' and release it accuretely instep with that time channel.

For clearness of diagrammatic representation, we have shown wheels |60,|6l, and |62 and wheels i12, |13, and |16 with progressively increasingdiameter; but in practice we prefer to make all these wheels of equaldiameter.

When released as described, sleeve |1| advances for one revolution insubstantial synchronism with the time channels of line current. Duringthis revolution dial switch 6| establishes three local channels p, q andr, for report symbols; and cam acting through follower |16 and rockshaft 11 releases pawl |18 and thereby establishes one mechanicalchannel, viz: channel 1', for receiving a control symbol. 1

@t6 is a second sleeve loosely mounted upon ait |66. Attached to thissleeve there are three wheels |18. |88, and iSi, and a triple contactbrush |89. This assemblage is driven by a spring lli? attached to a hub|82 which is frictionally driven by the shaft, so that the spring alwayswound and ready to advance sleeve |86 nidly whenever the latter is notrestrained. W eel l8| is normally held at one of six positions hv thepawl llt until the latter is released, as already described, at channelT. If the current received by polar magnet |63 during this time channeiis positive, pawls |83 and |84 will retain ions in which they are shown,with the till locking wheel |19. No movement of 986 will occur, and th-etriple brush |89 continue to contact with its upper segment, maintain acircuit from battery I9 to local wire |61, which may be the normaloperating wire for a track switch or some other operating unit. On theother hand, if current through the polar magnet |63 is negative duringtime channel r, the position of pawls |83 and |84 ill reverse. Sleeve|86 will advance 60 and me to rest with pawl |84 engaging wheel |80, aithe battery connected through brush |89 to the lower contact segment,supplying current to wire ist. This Wire may operate the track switch toits reverse position. In either case pawl |18 will again engage wheel|8i before the succeeding time channel, and will thereby maintain thestatus quo until the next recurrence of channel r in a cycle whichincludes the calling code for this substation. Other units similar tosleeve |86 and the associated parts may be provided Jfor other channelssuch as ,o and q, and may be jointly controlled by the one magnet |63.

It will be readily recognized that the contact brush |66 with itscontrolling elements is functionally equivalent to a polarized relay anda dial switch segment, since it selects and holds one oi two contacts inaccordance with the polarity of line current during a particular timechannel. The mechanical contacts described have certain advantages inthat several contacts may be controlled during successive time channelsby the same magnet, and in that contact movement and pressure arederived from local energy and are not limited by the energy which can betransmitted over the control line. Hence, we prefer to design thecontacts with suicient capacity to control the local operating circuitsdirectly without intervention of secondary relays or contactors.

The upper portion of Fig. il shows the local circuits at the centralstation over which current is supplied to one signaling channel T. Itwill be understood that similar circuits extend from each oi segments :ito r on each oi the dials 2| to 23 to the positive and negativeterminals of battery 66; but the battery and two alternators |42 and |63are common to all of the channels. Each signaling segment is connectedto the middle fixed Contact of a corresponding control switch 55. Theright and left xed contacts, respectively, are connected to the negativeand positive poles of battery' E4, while the centre of the battery isconnected through alternators |66 and |42 to ground.

For each segment and its associated control switch there is a network asshown connected between the blades of the control switch. When thelatter is thrown to the left, direct current flows from positive batteryto the left switch blade, and thence from left to right through thenetwork to the right-hand switch blade, whence it flows over the dialswitch segment to the line 6. This may be regarded as the positivedirection of current in the line, constituting one of the two irectcurrent symbols which may be transmitted over the line. The othersymbol, viz: negative current flow is transmitted when the controlswitch SE is thrown to the right. Current then hows outward from thecentre of the battery through alternators M3 and 42 to ground, and thereturn current reaching the central station over the control line iipasses through a dial switch segment (which, for the channel illustratedwill be segment r) to the left-hand blade of control switch 55, andthence from left to right through the network to the right-hand switchblade and the negative pole oi battery 5d. It should be observed thatreversal of control switch reverses the direction of current flow in thecontrol line 6, but does not change the direction of fiow through thenetwork which is from left to right in either case. Thus the controlswitch determines the polarity of current in control line Q during timechannel r and thereby determines the local control circuit |31 or |38which will be selected by contact device |89 at a certain substation;but it does not ailect the network, which comprises the receivingIelements for report symbols over channel r.

The network includes three branch paths from left to right, joined attheir midpoints by a tie conductor |56. The first path includes coils|44 and |41 and reactors |45 and |46; the second path, condensers |50and |5|; and the third path, coils |52 and |55 and rectifers |53 and|54. Of these paths only the rst is conductive for battery current, thesecond being blocked by condensers and the third by rectiers opposed tobattery current flowing from left to right. |48 is a polar relay Contactresponsive jointly to the coils |44 and |52, and |49 a polar relaycontact responsive jointly to the coils |41 and |55. These contacts maycontrol indicating lamp circuits similar to those shown in Fig. 6 forthe relays 46 and 41. When actuated by battery current flowing throughthe upper coils only as described, both contacts move to the left asshown.

Superposed upon the battery potential are 500 and 750 cycle alternatingpotentials induced by the alternators |42 and |43, respectively. Theresulting alternating components of current in the line are dependentupon the impedance of the line and connected branches. As alreadymentioned, the magnet coils at each substation are bridged by acondenser |51 offering little impedance to alternating current of eitherfrequency, so that the line impedance at any given substation is kept assmall as possible. The ground connection for direct current at the endof the line is made through a network consisting of two meshes |58 and|59. These two meshes are tuned substantially to prevent the passage of500 and 750 cycle currents, respectively. Hence the alternating currentin the line is substantially limited to that which can ow through abranch circuit at some substation. During time channel r, such a branchmay be established at one substation through dial switch 6| and reportswitch |33. The latter may be actuated by the track switch which iscontrolled during the same time channel by control wires |31 and |38.The centre position (as shown) of the report switch may indicate thatthe track switch is unlocked, and may open the branch circuit. In thiscase no appreciable alternating current will flow into th-e line duringtime channel r. If the track switch is locked in its normal position,the report switch may establish a branch path to ground through acircuit ISI', tuned to offer little impedance to 500-cycle current, buthigh impedance to 750- cycle current. A substantial 500-cycle componentof current will then flow into the line during time channel 1'. When thetrack switch is locked at its reverse position, report switch |33 mayestablish a path |62', tuned to pass a substantial 750- cycle component,but no material 500-cycle current. Thus, according as the track switchis normal, reversed or unlocked, there will flow into the line duringtime channel r a substantial 500- cycle current component, a substantial'750-cycle component, or neither. It should be noted that the branchcircuits IBI and |62 are blocked for direct current by condensersincluded in both circuits.

The mesh |56, |50, |44, of the receiving network is tuned to offer veryhigh impedance to 500-cycle current, but low impedance to 750- cyclecurrent. Accordingly, a substantial 500- cycle current ilowing intoy theline will cause a large drop oi potential in this mesh, which will beimpressed upon the branch path comprising tie |56, rectifier |53 andcoil |52. The coil |52, the voltage induced by 500-cycle alternator |42,and the circuit constants are so chosen that,

under this condition, coil |52 will overbalance coil |44 and cause thecontact |48 to reverse. In like manner, the mesh |56, |5|, |41, and |46is tuned to oppose the ovv of '750-cycle current and thereby cause thecoil to reverse the contact |49 when a substantial current of thisfrequency ilows into the line. Thus, either one of the contacts |48 and|49, or neither, may reverse during the contact period at segment 1',according as substantial current of 500 cycles or 750 cycles or neitherflows into the line; and hence, according as the track switch is normal,reversed or unlocked.

As described, a single channel 7' is capable of transmittingsimultaneously the necessary control symbol to govern the operation of atrack switch and the necessary report symbol to indicate its actualposition. In like manner, two channels may govern a group of signalsoperating in three positions; and one of these channels may indicate atthe central station the actual attainment of either position. Ihe otherchannel may indicate the position of a track relay. Thus, three timechannels, p, q, and r, surrice for transmitting all necessary controland report signals for one typical substation as shown in Fig. l. In thesame manner, channels y', 7c, and l, and channels m, n, and o, of cycle2|, may be used for communication with two other substations; or controland report symbols may be exchanged with three substations in all duringone revolution of either dial at the central station. If the dials areadjusted to complete one revolution in 0.4 second, control symbols maybe sent and report symbols received from any given substation withinthis interval by manually setting dial switch 3| to the desired cycle.Since the control and report symbols are simultaneous, the latter willindicate the initial position of the operated units, not the positionthey may assume in response to the control symbols. Completion of thedesired operation will be reported during the rst recurrence of the samecycle after the actual completion of the operation. If desired, dialswitch 3| may be held stationary, causing repetitions of the same cycleuntil completion of the operation has been reported. In this case, thereport will be received within fourtenths second after actual completionof the operation. If the automatic programas det/ermined by dial 3| isnot interrupted, communication both ways will be established atintervals, depending upon the number of cycles included in the program.For example, thirty-live cycles would provide for 105 substations. At aspeed of one cycle per 0.4 second, the positions of operating units ateach substation would be reported every 14 seconds. Control symbols, asdetermined by the positions of control switches such as 55, would bereaiirmed at like intervals, but would change the local control circuitsat the substation only when the positions of control switches had beenchanged. In effect, the operating units will be continuously responsiveto the position of the control switches with a possible time lag of 14seconds, and will continuously report to the central station With a liketime lag.

In Fig. l1 We have shown a duplex system in which control signals andreport signals are transmitted simultaneously over the same channels,but the same type of cycle, comprising a substation call followed bycontrol or report signals, is equally adaptable tc other signalarrangements. For example, as in Fig. 6, and as described hereafter inconnection with Fig. 13, the automatic program may consist of reportsymbols only, or

of control symbols only, and provision may be made for manualinterruption of the one class of signals and substitution of the otherclass. Furthermore, the particular choice of symbols we have describedis largely arbitrary. We have described for substation calls a code ofpositive and dead channels; for control symbols, positive and negativedirect current channels; and for report symbols, 50G-cycle and'Z50-cycle alternating current or neither. But the same current symbolscould equally Well be distributed in other ways among the samefunctions. For example, if the polar magnet |63 and the neutral magnet69 are interchanged, and the former biased to take its positive positionwhen deenergized, calling signals may be given by negative and zero ornegative and positive currents, and control signals may be given bypositive and zero currents. Or with suitable modifications of the pawlsand of the symbols transmitted by the central station, polar magnet |93may be replaced by a neutral magnet shunted by a rectier to render itunresponsive to current of one polarity and magnet 69 may be shunted bya rectiier to render it unresponsive to current of the oppositepolarity. The only essential limitation on the assignment of symbols forcalling, control signals and report signals, is that wheels |69 and |12shall engage their pawls throughout the group of time channels assignedfor control and report symbols, and wheels and lli-l shall engage theirpawls at certain other times as required for response to callingsignals. In the code described, zero current is a symbol reservedexclusively for calling signals, but any other one symbol may bereserved for the same purpose.

The specific cycle described in which nine channels are assigned forcall signals and nine for control and report signals, is advantageous inthat it permits control of a large number of substations withoutinvolving synchronism over a longer period than nine time channels fromany given start; but many other assignments 'of channels are obviouslypossible, for example, eight time channels for calls and twelve, or`three substation groups, for control. This combination permitsdistinctive calls for twenty groups of four substations, eightysubstations in all. The num- -er of calling channels may be less thanthe number of control channels, but should not be more, because thereceiving device for calls must reach its starting point from anyposition within the period assigned to control signals.

Fig. lf2 shows a modification of Fig. l1 in which polar magnet winding|63 is replaced by two opposed windings |53 and |635, and neutral magnetwinding |59 is replaced by two windings 69 and $92. The windings |63 and59 are energized by pulsating current derived from transformer winding|921 and controlled by an electric discharge relay or valve |92.Windings |53.a and 69a are energized by transformer winding |93, subjectto control by a discharge relay or valve |9fi. |95 is a primary Windinginducing potential in both secondary windings |9| and |93. |99 is asource of alternating current, and may be, for example, a pair of sliprings connected to the armature of a high speed direct current motorconnected through reduction gearing to drive receiver shaft |55 (Fig.11).

The valves |92 and 196i are of a relay type such as the socalledThyratron. They are characterized by the fact that current starts in theplate circuit only when the grid potential, with respect Y to thelament, is above a certain critical value,

but that plate current once started will persist irrespective of gridpotential until the succeeding Zero point of the plate current Wave.Alternating potential as described is applied to the plate circuit inorder that such zero points may occur at frequent intervals; and inorder that the times of current start and interruption may approximatelycoincide with the make and break times at the central station dialswitches, the frequency impressed on the plate circuits should berelatively high, insuring several positive half waves during each timechannel. A bias battery |9l is included in the grid connection of eachvalve and adjusted to prevent the flow of plate current during deadchannels with the line at ground potential. Each valve is furtherprovided with a lament battery |98.

The filament of valve |92 is grounded and its grid is connected tocontrol line 9. When the potential of the latter is positive, currentwill iiow through the plate circuit and through magnet coils |63 and|59, producing the same effects as positive line current through thecorresponding coils in Fig. ll.

The grid circuit of valve |9l| is grounded, and the filament isconnected to the control line. When the line is negative with respect toground the grid becomes relatively positive. Current Hows through theplate circuit and through coils Milla and 69a, producing the sameeffects as negative line current in the corresponding coils of Fig. 11.

In order that positive or negative peaks in the alternating componentsof line potential may not cause current to flow through the platecircuits of the valves, the potentials of central station battery 54,bias batteries |91, and alternators |42 and |43 must be so coordinatedthat the grid potential of one valve or the other will be below thecritical value required to start plate current throughout the pulsationsof the resultant line potential.

It is to be observed that the iilament to grid circuits of the valves|92 and |94 constitute branch circuits from the line to ground, and thattwo such branches are always connected to the line at each substation.It was previously stated that the high resistance of the line and thelimited resistance for which coils can conveniently be wound made thistype of multiple circuit undesirable for coils connected directly to theline. Gwing to the exceedingly high resistance of the grid circuits inthe valves, the same objection does not obtain in Fig. 12. Since thegrid circuits are controlled by line potential rather than line current,the ground connection through network Mii-|59 at the end of the line isunnecessary in the present case.

in Fig. 13, we show another modification in which all control signalsrequired for one substation are embraced within a group of seven timechannels, each individual signal comprising two live channels and ivedead channels, The codes are soI arranged that they may overlap withoutconflict; for example, if channels to 'l are assigned to substation 2,channels 2 to 8 may be assigned to substation 3, and channels 3 to 9 tosubstation 4; but no substation will respond to signals transmitted forany other of the substations which have certain channels in common. Acycle of N time channels provides codes for N substations; but the lastcode overlaps the beginning of the cycle by six channels. Any controlsymbol may be initiated at any time and will be completed whenever thenecessary time channels become available thereafter. If initiatedcoincidentally with the first of the required time channels, the signalwill be completed within a space of seven time channels. If initiated atthe most unfavorable point in the cycle it will be completed Within aspace of N plus 6 time channels.

Control signals are transmitted exclusively by negative currentimpulses. At all times when such signals are not being transmitted, aprogram of positive impulses is automatically transmitted, and reportsignals are thereby received from each operating unit of everysubstation in rotation. The report program occupies three time channelsper substation, and when the line is not in use for control signals,reports are received from all operating units within a period of 3N timechannels, or the equivalent of three control signal cycles.

In Fig. 13, parts 29 to 52 are receiving elements at the central stationfor report signals. They are identical with the corresponding parts inFig. 6, save only that in Fig. 13 the dials 2| and 22 have segments foreach time cycle of the whole program and select directly the relays 46and 41 for retaining report indications, whereas in Fig. 6 thecorresponding selection was eifected jointly by dials 2| and 22 anddials 3| and 32. As drawn, each of the dials 2| and 22 has forty-eightsegments, suficient for sixteen groups of three segments per substation.It is to be understood that relays 46 and 4`| of Fig. 13 may controlindicating lamps as shown in Fig. 6. Thus, in the absence of manualintervention, dials 2| and 22 will maintain a continuous program of 48time channels, and during each time channel one group of indicatinglamps may be controlled, showing the position of one operating unit at asubstation. The indications of each group of lamps will be broughtup-to-date at intervals of 48 time channels, or about one second if thedials are operated at a speed of fty channels per second.

In Fig. 6, switches 34, 35, 49, and 56 were provided to select receivingcircuits for report signals or sending circuits for control signals. InFig. 13 the same function is effected by a drum controller 293 mountedupon the shaft 29 and frictionally vdriven thereby. A two-point ratchet|99 and a pawl 299 normally hold the controller at one of two normalpositions in which the control line 9 is connected to the receivingcircuits and relay coils 46 and 41 are connected to ground. Bydepressing a push button shown on pawl 299 the latter may be released.Ratchet |99 and controller 293 will then advance one-half revolutionwith shaft 29. During this time the line 9 is connected for a period of22 time channels or more to the sending circuits instead of thereceiving circuits and the ground connection from relays 46 and 41 isbroken to prevent any change at the indicating lamps during the timethat their control over line 9 is interrupted.

While the controller 293 is travelling between one normal or receivingposition and the next,

each connected substation. This brush arm is geared to shaft 29 andmakes three revolutions for each revolution of the latter, so thatcontacts are made simultaneously at dial 24 and at dials 2| and 22; butcontact is made at each segment of dial 24 during three different timechannels as established by dials 2| and 22.

From the segments of dial 24 five connections lead to each substationpanel, such as |3 or I4 in Fig. 1, terminating on the control switchesfor signals and track switch machines. These connections are indicatedonly for control switches 53 and 55 of substation panel I3 and controlswitches 53fL and 55a of substation panel |4. The complete circuitswould include five connections from each segment of the dial switch.

29| and 292 are two dial switches mounted upon a common shaft andmanually operated. Both brush arms are connected to the negative pole ofbattery 54, the positive pole being grounded. Each segment of dial 29|is connected to the blade of the control switch 53, 53a, etc., on onesubstation control panel, and the corresponding segment on dial 292 isconnected to the blade of control switch 55, 55a, etc., on the samepanel. Thus, at a given time, the battery may be connected at will tothe control switches of one substation control panel and only one.Connections from the segments of dial 24 to all other substation controlpanels are then dead-ended as can be seen, for example, by tracingconnections from the dial through control switches 53u and 55a on panel|4. Thus the panel selected by dials 29| and 292 has exclusive controlof battery connections to dial 24. If preferred, it will be readilyunderstood that an equivalent group of relays may be substituted fordial switches 29| and 292, and that battery connections to any panel maythen be established by pressing a button on the panel.

When battery connections have been established to a given substationpanel, control switches 55 and 53 on that control panel will completepaths, respectively, to one segment selected among an assigned group oftwo on dial switch 24, and to one segment selected among another groupof three. As described hereafter, the receiving relays at thecorresponding substations are so connected that they respond only whenone negative impulse is received during each of the corresponding groupsof two and three time channels, respectively. If channels of therespective groups are indicated by capitals and small letters, thegroups for one substation may be assigned according to one of thefollowing two arrangements: ABceg, or ADefg. In either case, each choiceof one capital and one small letter is peculiar to a single substationand cannot be duplicated in any overlapping group similarly assigned.Connections shown in Fig. 13 are according to the first arrangement. Thecomplete list of channel assignments for sixteen substatio-ns, involvingsixteen channels lettered from a to p, is as follows:

Substation 1 2 3 4 5 6 7 8 l0 l1 12 13 14 15 16 Channel A B C D E F G HI .T K L M N O P B C D E F G H I J K L M N O l A c d c f g h i j l: l mn o 7) a b e f g h i j k L m 'n a p a b c d g h i j k l m n o p a h c de f control line 9 is connected to the brush arm of dial 24, which hassixteen points, one point for Among the capital letters it will be notedthat substation includes A in common with substa-

